Fourteen former national security, intelligence, and foreign policy officials recently wrote an amicus brief as part of a lawsuit brought against President Donald Trump's campaign and Roger Stone, his longtime adviser.

Among the former officials are John Brennan, a CIA director; James Clapper, a director of national intelligence; and Michael Hayden, a director of the National Security Agency.

The brief explained how the Kremlin used local actors to help amplify the scope and impact of its influence operations, including the one targeting the US election in 2016.

Fourteen former national security, intelligence, and foreign policy officials who have served at senior levels in Republican and Democratic administrations recently wrote an amicus brief as part of a lawsuit brought against President Donald Trump's campaign and Roger Stone, his longtime confidant.

The lawsuit was filed in July by three private citizens — Roy Cockrum, Scott Comer, and Eric Schoenberg — whose personal information was stolen in hacks of the Democratic National Committee and published by WikiLeaks. The plaintiffs have argued that the Trump campaign, Stone, "and those they conspired with arranged for the hacked information to be provided to WikiLeaks."

The Trump campaign and Stone have filed motions to dismiss the complaint. The plaintiffs responded on December 1, laying out, among other things, a "motive to collaborate" between the campaign and Russia, as well as points of contact.

Among the former officials who filed the amicus brief on December 8 are John Brennan, a CIA director; James Clapper, a director of national intelligence; and Michael Hayden, a director of the National Security Agency; Avril Haines, a deputy national security adviser; Michael McFaul, a US ambassador to Russia; and Michael Morell, an acting CIA director.

The former officials emphasized in the neutral brief that they could not disclose classified information. But their message was clear: The Kremlin uses local actors to help amplify the scope and impact of its influence operations, including the one targeting the US election in 2016.

The cutouts can range from "the unwitting accomplice who is manipulated to act in what he believes is his best interest, to the ideological or economic ally who broadly shares Russian interests, to the knowing agent of influence who is recruited or coerced to directly advance Russian operations and objectives," the former officials wrote.

Cutouts can be anyone, they explained, from journalists and academics to "prominent pro-Russian businessmen."

These local actors help the Kremlin further its foreign influence operations and "active measures" campaigns, they wrote. Those operations often involve the spread of disinformation and conspiracy theories and cyberattacks — all in an attempt to "undermine confidence in democratic leaders and institutions" and "discredit candidates for office perceived as hostile to the Kremlin."

This type of brief is 'certainly unusual'

It is "certainly unusual" for a group of such high-profile former officials to write and submit a brief to a district court, said Renato Mariotti, a former federal prosecutor.

But it is a way for the former officials to "draw attention" to an issue they believe is important for the public to understand, Mariotti said, even if the point they make "doesn't really move us far down the road to establishing a conspiracy."

Michael Carpenter, a former deputy assistant secretary of defense for Russia, Ukraine, and Eurasia who helped write the brief, said the goal was "to inform the court, and by extension the American public, about the subversive character of Russian 'active measures' campaigns."

"One of the key points we make," Carpenter said on Thursday, "is that active measures campaigns are almost always carried out using local actors who enable Kremlin agents to get closer to their target and gather information on how best to achieve their desired goal (for example, establishing a corrupt relationship that can be later exploited for purposes of blackmail or manipulation)."

Michael Flynn, the former national security adviser who was a top Trump campaign surrogate, pleaded guilty earlier this month to lying to FBI agents about the nature of his conversations last December with Sergey Kislyak, Russia's ambassador to the US at the time.

Paul Manafort, the campaign chairman, and his longtime associate Rick Gates were indicted in October on charges that included money laundering, tax fraud, and failure to register as a foreign agent. Much of their money, the government said in court filings, came from Ukrainian and Russian oligarchs.